Fire barrier system for multi-family dwellings

ABSTRACT

In a dwelling construction system, a multi-story, multi-family building comprises prestressed concrete pallets which are supported between load bearing walls to form the floors and the ceilings of individual dwellings. Each dwelling includes a service core comprising an enclosure formed on one of the pallets and complete mechanicals for the dwelling. The service cores are fabricated by mass production techniques and are subsequently transported to the building site for installation. In some instances the service core comprises a complete dwelling, in which case the enclosure of the service core may form the exterior walls and the roof of the dwelling.

iliiited States patent McQrillis et al.

1 1 Sept. ll, 11973 1 1 FIRE BARRIER SYSTEM FOR MULTl-FAMILY DWELLINGS[75] inventors: Raymond L. McCrillis; Walter T.

Fuller, both of Littleton; Richard H. Dixon, Lakewood; John F. Oldani,Littleton, all of C010.

[73] Assignee: Marcor Housing Systems,

Incorporated, Denver, C010.

[22] Filed: Mar. 1, 1972 [21] Appl. No.: 230,825

[52] US. Cl 52/79, 52/236, 52/317, 52/745 [51] Int. Cl E04b 1/94 [58]Field of Search 52/236, 79, 317, 5 2/404, 412, 262, 283, 745

[56] References Cited UNITED STATES PATENTS 293,617 2/1884 Bartlett52/317 3,162,863 12/1964 Wokas 52/79 Primary Examinerlohn E. MurtaghAttorney- D. Carl Richards. E. Mickey Hubbard et a1.

[57] ABSTRACT In a dwelling construction system, a multi-story,multifamily building comprises prestressed concrete pallets which aresupported between load bearing walls to form the floors and the ceilingsof individual dwellings. Each dwelling includes a service corecomprising an enclosure formed on one of the pallets and completemechanicals for the dwelling. The service cores are fabricated by massproduction techniques and are subsequently transported to the buildingsite for installation. In some instances the service core comprises acomplete dwelling, in which case the enclosure of the service core mayform the exterior walls and the roof of the dwelling.

9 Claims, 28 Drawing Figures PATENTEBSEPI nan saw our 15 PATENTEIJ SEPII 975 sum 02 or 7s PATENTED SEP'! 1 I975 sum 03 or 15 FIG. 7

PATENTED SEPI I I973 SHEET 0Q [1F 15 PATENTED SEP] 1 I975 sun-:1 us or15 FIG. I!

PATENTED SEP] 1 I975 sum 08 a;

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PATENTED SEP] 1 I973 sum as or 1 PATENTED SEP] 1 I973 SHEET 11 [1F 15PATENTED SEP] 1 I975 SHEET 12 0F 15 FIG. I7

SHEET 13UF 15 FIG. 2/

PATENTEUSEPI 1 I973 FIG. 20

PATENTEDSEPY 1 I915 $151.41?

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PATENTEDsEPn'ms- 3,757, 477

sum 150F15 FIG. 24 FIG. 25.

SYSTEM FOR MULTI-FAMILY DWELLINGS BACKGROUND AND SUMMARY OF THEINVENTION This invention relates to dwelling construction systems, andmore particularly relates to a system for fabricating a wide range ofdwelling types using production line techniques.

Very substantial sums of money have been expended over the last decadeor two to develop building systems which use production line techniquesin the construction of both single family and multi-family dwellings.The basic considerations fueling this activity are rapidly increasinglabor costs of tradesmen, and the hope that use of production linemanufacturing procedures would reduce or eliminate the need for thehighly skilled labor of tradesmen as well as provide other cost savings.

This type of construction is particuarly promising in the case ofdwellings to be erected at remote or relatively inaccessible buildingsites where labor and materials are not readily accessible.

To date the most successful adaptation of production line techniques todwelling construction has been in the mobile home industry. As is wellknown, the fabrication of a trailer house, including the installation ofmechanicals such as kitchen, bathroom, and temperature controlfacilities, is typically carried out to completion at a factory. By thismeans the labor required to install such a dwelling at a particular siteis reduced to an absolute minimum.

A different but related method of adapting mass production to dwellingconstruction comprises sectionalized houses. Typically half or quarterhouse sections are fabricated at a factory using conventional buildingmaterials and techniques and are transported to a construction site bytruck. At the site the sections are positioned adjacent one another andare joined to form a completed house.

Multi-family dwelling units have also been considered using productionline techniques. By ay of example, one construction system that has beenused heretofore involves the fabrication of box-like modules eachincluding a floor, walls and a ceiling which are interconnected to forma structurally integral and transportable unit. The finishing of themodules, including the installation of mechanicals, is completed at afactory. Thereafter the modules are transported to a construction siteand are stacked in various configurations to form dwelling units. Inthis case, the interrelationship of the floor, walls and ceilings ofeach module cooperates to provide the structural integrity and loadbearing capacity necessary to permit the modules to be transported andhandled. This type of system has the inherent disadvantage of greatlylimiting flexibility of design, and also results in duplicate wallstructures.

Although the modular building systems heretofore used have provided somecost reduction, the systems are inherently inflexible and greatly limitthe architectural design and livability of the structures. In general,the greater the modularization of the system to achieve reduced costs,the more inflexible the system is to design change, the smaller therooms, and the more unlivable the dwelling.

Another trend in the construction industry involves the use ofprestressed concrete structural components.

FIRE BARRIER Thus, structures such as bridges, parking garages,warehouses and the like are presently being fabricated from variousprestressed components including load bearing and non-load bearingwalls, columns, beams, and floor and roof decks. I-Ieretoforeprestressed members have been used solely as structural elements. Thispractice necessitates the use of labor at the construction site toperform such tasks as erecting interior partitions, installingmechanicals, etc.

The present invention comprises a novel dwelling construction systemwhich incorporates many of the advantages that are characteristic ofprior art modular construction systems while eliminating substantiallyall of the disadvantages that have long been associated with suchsystems. In accordance with the broader aspects of the invention, aservice core is substantially completely fabricated on an assembly lineusing mass production techniques. The service core is formed on aprestressed concrete pallet which is also fabricated at a plant siteusing automated equipment for greatest economy. The service coreincludes a mechanical enclosure which may be fabricated fromconventional drywall building materials of the type used in buildinghouses, and similar buildings. The mechanical enclosure may includecomplete mechanicals for at least one dwelling, i.e., complete kitchenfacilities, complete bathroom facilities, complete temperature controlequipment, and electrical systems including telephone and televisionwiring.

Upon completion, each service core is transported to a dwelling site.The concrete pallet provides the only struc-tural integrity required,thus giving total flexibility in the design of the enclosures. In someinstances the service core may comprise an entire dwelling. More often,however, each service core is employed in conjunction with additionalprestressed concrete pallets to form a relatively large dwelling. In thelatter case the pallets extend between and are supported by prestressedconcrete load bearing walls to provide a clear span of substantiallength. Additional combinations of service cores and pallets may also besupported on the load bearing walls to form garden apartments, high riseapartments, and the like.

In accordance with more specific aspects of the invention, theprestressed concrete pallets used in the service cores and used inconjunction with the service cores to construct dwellings each comprisea relatively thin deck, a plurality of integrally formed beams dependingfrom the deck, and pretensioned members extending through the beams toprestress and maintain the concrete of the beams in compression suchthat the beams are adapted to span a substantial distance between twospaced load bearing points and still support large static and live loadson the deck. The deck may terminate at the load bearing points, in whichcase the deck is entirely enclosed by the load bearing walls. On theother hand, the beams may be cantilevered substantially beyond either ofthe load bearing points to support a deck portion located outside theload bearing walls to provide a balcony, an entry corridor, etc.

In the use of the present invention to construct a multi-family dwellingsuch as a garden apartment, a pair of load bearing wall panels areinitially erected at points spaced in accordance with the positioning ofthe support points of the beams of the concrete pallets. After the loadbearing wall panels are in place, a service core and then one or moreadditional pallets are set in place on the load bearing wall panels toform the floor of a first story dwelling. in the case of the first floordwelling, the beams of the pallets may rest on members projectinginwardly from the load bearing wall panels. Non-load bearing shear wallpanels interconnect the load bearing wall panels and serve the dualfunctions of enclosing the dwelling and maintaining the load bearingwall panels erect.

A service core and then additional pallets which form the ceiling of thefirst floor dwelling and the floor for a second story dwelling are setin place on the top edges of the load bearing walls of the first floorunit. The beams of the pallets of the second dwelling are preferablyreceived in notches formed in the upper ends of load bearing wall panelsthat enclose the lowermost dwelling. Also, the decks of the palletsforming the floor of the second dwelling preferably either end at or areinterrupted at points corresponding to the positioning of the loadbearing wall panels. This permits mounting a second pair of load bearingwall panels directly on the first pair of load bearing wall panels toform the walls for the second floor dwelling.

When the second set of pallets are in place, a second pair of loadbearing wall panels and a second pair of shear wall panels areinstalled. Then a third set of pallets including a service core for athird dwelling are mounted on the second pair of load bearing wallpanels to form a ceiling for the second floor dwelling and the floor fora third dwelling. This procedure is repeated until all of the dwellingsin the apartment are formed. Then prestressed concrete pallets aremounted on the uppermost load bearing wall panels to form the roof ofthe uppermost dwelling, and of the stack of dwellings. The interiors ofthe several dwellings are then grouted, and floor and wall coveringsinstalled, whereupon the structure is ready for occupancy.

As will be appreciated by those skilled in the art, prestressed concretepallets of the type employed in the practice of the present inventioncan be supported only at the two design load bearing points. In mostinstances, the blank pallets are handled by means of eyes cast in theconcrete. However, the pallets upon which the service core is formedmake this method of handling the pallets impractical. Accordingly, eachservice core is set in place by means ofa pair of picking bars whichextend under the support points of the beams of the pallet, a harnessincluding members for connection to the opposite ends of the two pickingbars, and ammo which operates through the harness and the picking barsto lift and position the pallet. On the other hand, both for fireprevention purposes and for the sake of appearance, it is highlydesirable that the enclosure of each service core extend substantiallyinto engagement with the pallet located next about the service core. Tothis end the enclosure of each service core is equipped with at leastone picking bar slot positioned to permit withdrawal of one of thepicking bars that will be used to install the service core or palletabove the service core. The picking bars used in the installation of thepallets weigh approximately 400 pounds. This necessitates reinforcingthe picking bar slots to such an extent that the picking bar does notdamage the service core as it is withdrawn.

The building codes of the various cities and states typically require afire barrier having a one hour rating between adjacent buildings in amulti-family dwelling. In the practice of the present invention thisrequirement is easily fulfilled with respect to pallets that do notcomprise service cores by simply filling the spaces between the decks ofthe pallets and the load bearing wall panels and the shear wall panelswith grouting. On the other hand, the enclsoures of the service coresprevent access to these spaces and thereby prevent the filling of thespaces with grouting. For this reason the service cores are preferablyinstalled with one edge of the deck engaged with the adjacent wallpanel. At the other end of the deck a strip of sheet metal is securedbetween the enclosure and the deck. The strip of sheet metal is extendedover the upper edge of the load bearing wall panels that supports thedeck and is engaged by the load bearing wall panel that is mounted onthe supporting panel to provide the necessary fire barrier.

In accordance with a particular embodiment of the invention, doubleloaded service cores are utilized in the construction of adjacentdwellings. That is, a single prestressed concrete pallet is equippedwith two complete but separate sets of mechanicals, one for each of theadjacent dwellings. in such a case it is necessary to form a firebarrier having a one hour rating between the portion of the service corethat is individual to one of the dwellings and the portion that isindividual to the other dwelling.

The majority of the fire barrier for a double loaded core may comprise awall including at least one layer of inch sheet rock. A pair ofdiverging sheet metal flanges are provided at the upper end of this wallfor engagement with a beam of the pallet that is installed above thedouble loaded core to form the upper portion of the fire barrier. Thefire barrier wall is also provided with a stub wall which is slidablysupported at the end of the deck that will be engaged with a loadbearing wall. During installation of the double loaded core the stubwall is retracted. Then, after the load bearing wall panels adjacent thedouble loaded core have been installed, the stub wall is moved outwardlyand is engaged with the adjacent load bearing wall panel. By this meansthe fire barrier between the portions of the double loaded core that areindividual to the separate dwellings is extended to the full height andthe full width of the core.

In addition to the foregoing, the present invention incorporatesnumerous features which contribute greatly to its overall practicality.For example, notwithstanding the strength of prestressed concretepallets, it has been found that a direct connection between a particularpallet and the enclosure of a service core situated beneath the palletis not workable. lnstead a slip joint is employed to provide a pleasingappearance while permitting relative movement between the pallet and theservice core as a result of live loads.

Another important feature of the invention involves the manner in whichconvenience outlets are provided at spaced points around each dwelling.Thus, electrical conduits are formed in the load bearing wall panelswhen the panels are manufactured. After the panels are installed,electric service lines are directed from the adjacent service coresthrough the conduits in the load bearing Wall panels and along the shearwall panels. The shear wall panels are typicaily covered with woodpanelling or the like, so that the resulting dwelling is equipped withsuitable convenience outlets and yet has no exposed conduit or wiring.

Still another important feature of the invention involves an improvedmethod of forming the enclosures of the service cores. It has been foundthat a great deal of time is wasted if the enclosures are formed byfinishing the walls on one side, installing the walls on the pallet byfastening through the panel frame into the pallet, and then finishingthe walls on the other side of the panel. In accordance with the presentinvention holes are formed in the pallets along the lines that willcomprise the walls of the enclosures. This permits the walls to becompletely finished and then secured to the pallets by means of lagscrews which are inserted through the holes in the pallets from thebottom.

DESCRIPTION OF THE DRAWINGS A more complete understanding of theinvention may be had by referring to the following Detailed Descriptionwhen taken in conjunction with the accompanying Drawings, wherein:

FIGS. 1-7 are illustrations of progressive steps in a method offabricating dwelling units incorporating the invention;

FIGS. 8 and 9 are illustrations of presetressed concrete palletsutilized in the practice of the invention;

FIG. 10 is a view taken generally along the line l0l0 in FIG. 5 in thedirection of the arrows;

FIGS. 11 and 12 are perspective and end views, respectively, showing amethod of and apparatus for installing service cores which is utilizedin the practice of the in-vention;

FIG. 12A is an end view of an alternative type of prestressed concretepallet that can be utilized in the practice of the invention;

FIG. 13 is an elevational view of an apartment complex constructedin-accordance with the invention;

FIG. 14 is a plan view of the apartment complex shown in FIG. 13;

FIGS. ISA-15C are an enlarged plan view of one of the apartmentscomprising the apartment complex shown in FIG. 13; I

FIG; 16 is an enlarged plan view illustrating the service core of one ofthe apartment buildings shown in 'FIG. 14;

FIG. 17 is a sectional view taken generally along the line 17-17 in FIG.16 in the direction of the arrows;

FIG. 18 is a sectional view taken generally along the line l818 in FIG.16 in the direction of the arrows;

FIG. 19 is an enlargement of the upper portion of FIG. 18;

FIG. 20 is a sectional view taken generallyalong the line 2020 in FIG.16 in the direction of the arrows;

FIG. 21 is an illustration of special slots which are utilized in thepractice of the invention to facilitate the installation of prestressedconcrete pallets on previous-ly DETAILED DESCRIPTION METHOD OF DWELLINGCONSTRUCTION Referring now to the Drawings, and particularly to FIGS.l-7 thereof, a method of dwelling construction incorporating the presentinvention is employed to construct an apartment building 48. As is bestshown in FIG. I, the first step in the method comprises the erection ofa pair of load bearing wall panels 50 and 52. The wall panels 50 and 52are both formed from prestressed concrete and are both nominally sixinches thick. The wall panels 50 and 52 are further similar in that theyare both provided with a plurality of slots or notches 54 formed in theupper ends and with a plurality of support members 56 which projectinwardly from points adjacent their lower ends. The notches 54 aregenerally U-shaped, but comprise inwardly tapered side walls, and someof the notches 54 in the wall 50 extend only part way through the wallso as to provide a flush outer surface. The supporting members 56 maycomprise any convenient construction, but preferably comprise pipe stubscast into the panels 50 and 52 and extending inwardly therefrom. Onedifference between the wall panels 50 and 52 is that the wall panel 50is provided with a door opening 58.

Referring now to FIG. 2, the next step in the method of dwellingconstruction comprises the installation of a service core 60. Theservice core 60 comprises a prestressed concrete pallet 62 and anenclosure 64 formed on the pallet 62. The service core 60 furthercomprises complete mechanicals" for a dwelling unit, i.e., completekitchen facilities, complete bathroom facilities, and completetemperature control facilities.

The prestressed concrete pallet 62 of the service core 60 is shown inFIG. 8. The pallet 62 comprises a deck 66 and three beams 68 whichdepend from the deck 66. Thus, the pallet 62 isof the type commonlyknown as a triple T deck. A plurality of tension members extend througheach beam 68 of the pallet 62 and serve to prestress the beams, wherebythe beams 68 are adapted for support at spaced points indicated by thearrows 72 to support a load on the deck 66. As is well known in the art,a prestressed concrete pallet of the type shown in FIG. 8 is subject tobreakage unless it is properly I supported. g l

The cross sectional configuration of the pallet 62 is shown in FIG. 12.Those skilled in the art will appreciate the fact that the invention mayalso be practiced using either solid core or hollow core prestressedconcrete pallets 62' of the type shown in FIG. 12A. The pallet 62'comprises a deck 66 and a plurality of beams 68' which depend from thedeck 66' between cylindrical passageways 69'. A plurality of tensionmembers 70 extend through a lower portion 7l One difference between thepallet 62 and the pallet 62' is that whereas the beams 68 of the pallet62 are exposed, the bottom of the pallet 62 is flat.

Referring again to FIG. 2, the enclosure 64 of the service core 60 isformed on the deck 66 of the prestressed concrete pallet 62. Theenclosure 64 is preferably formed from materials of the type used inconstructing conventional homes and similar buildings, i.e., two by fourand two by six studs, drywall panels, and similar materials. Theenclosure 64 includes interior partitions which separate the variousmechanicals of the dwelling unit into kitchens, bathrooms, and the like,and further includes at least one end wall .and a'dropped or falseceiling 76.

In accordance with the illustrated embodiment of the invention, theservice core 60 is completely fabricated at a factory by means of massproduction techniques. The fabrication of the core 60 comprisesconstruction of the walls, partitions, and ceilings in suitable jigs andfixtures, installation of the walls, partitions, and ceilings,installation of all mechanicals, installation of electrical, plumbing,and heating/air conditioning risers for the mechanicals, installation ofall doors and cabinetry,

installation of floor and wall coverings, and painting. Thus, when theservice core 60 is installed between the load bearing wall panels 50 and52, it is complete and ready for use. This feature of the invention ishighly advan-tageous in that it not only reduces the cost of a dwellingby applying mass production techniques to the construction of theservice core, but also reduces the time that is required to finish adwelling following the beginning of construction at the dwelling site.

Upon completion of the manufacture of the service core 60 at thefactory, it is transported to the site of the building 48 by truck.During such transportation, the service core 60 is supported solely atpoints corresponding to the support points of the beams. This isaccomplished by means of members positioned under the support points ofthe beams to maintain the remainder of the pallet out of contact withthe bed, etc. of the truck.

The service core 60 is installed by means of apparatus of the type shownin FIGS. 11 and 12. A pair of picking bars 78 are positioned under thebeams 68 of the pallet 62 at points corresponding to the support pointsof the beams. The picking bars 78 are engaged by a harness 80 comprisinga plurality of cables 82 and a spreader frame 84 which functions tocause the cables 82 to extend vertically upwardly from the picking bars78 to points above the enclosure 64 of the service core 60. The cables82 are connected to a beam 86 which is in turn supported by a cable 88extending from a crane (not shown). By this means the crane functionsthrough the harness 80 and the picking bars 78 to lift and position theservice core 60.

Referring again to FIG. 2, the service core 60 is installed between theload bearing wall panels 50 and 52 with each beam 68 of the pallet 62engaged with one of the support members 56. It will be appreciated thatdue to manufacturing tolerances and in order to facilitate theinstallation of the core 60 between the wall panels 50 and 52, thelength of the pallet 62 is necessarily somewhat less than the distancebetween the interior surfaces of the walls. The resulting gap isaccommodated by positioning the deck 66 closely in engagement with thewall panel 50, whereupon a suitable entry in the enclosure 64 is alignedwith the door opening 58 in the wall'panel 50. This forms a small gapbetween the deck 66 and the wall panel 52. However, an end wall isprovided at the end of the enclosure 64 remote from the door opening 58,whereby the gap is not visible from within the service core 60.

The next step in the method of dwelling construction comprises theinstallation of a pair of blank prestressed concrete pallets 90 betweenthe lead bearing wall panels 50 and 52. The pallets 90 are handled bymeans of cables 92 which are connected to eyes 93 in the pallets. Thesame procedure could be employed in handling service cores except thatthe enclosures of the service cores prevent access to the eyes of thepallets. Thus, the service cores must be handled by means of pickingbars.

The blank pallets 90 are identical to the pallet 62 of the service core60 in that they each comprise a deck, three beams depending from thedeck, and tension members extending through the beams for prestressingthe pallets. The pallets 90 are positioned between the wall panels 50and S2 with their respective beams engaged with the support members 56of the walls. The decks of the pallets are therefore aligned with thedecks 66 of the pallet 62, whereby the pallets 90 cooperate with thepallet 62 to form the floor of a dwelling unit.

As is best shown in FIG. 4, the installation of the pallets 90 isfollowed by the installation of a pair of shear wall panels 94 and 96.The wall panels 94 and 96 are formed from prestressed concrete, butdiffer from the load bearing wall panels 50 and 52 in that they arenominally four inches thick. The shear wall panels include windowopenings 98 and a door opening 100 and serve the dual functions ofenclosing the ends of the dwelling unit and maintaining the load bearingwalls erect.

The shear wall panels 94 and 96 are preferably connected to the loadbearing wall panels 50 and 52 by forming welds between suitable memberswhich either comprise part of or are connected to the reinforcingstructure of the wall panels. The load bearing wall panels and the shearwall panels may also be joined by other techniques of the type commonlyemployed in the construction industry to connect prestressed concretestructural members. The various prestressed concrete pallets which areemployed in the practice of the invention may be connected to the loadbearing wall panels by similar techniques, however, it has been foundthat it is often unnecessary to connect the pallets to the load bearingwall panels in any fashion.

Upon the installation of the shear wall panels 94 and 96, the lowermostapartment of the apartment building 48 is structurally complete.Thereafter, a service core 102 for a second dwelling unit is mounted onthe load bearing wall panels 50 and 52. As is shown in FIG. 5, theservice core 102 com-prises a prestressed concrete pallet 104 and anenclosure 106 formed on the pallet 104. The service core 102 furthercomprises complete mechanicals for the second apartment.

The pallet 104 of the service core 102 is illustrated in FIG. 9. Thepallet 104 is similar to the pallet 62 in that it comprises a deck 108and three beams 110 which depend from the deck. A plurality of tensionmembers 112 extend through the beams 110 to prestress the beams andthereby adapt the beams for support at spaced points indicated by thearrows 114 to support a load on the deck 108.

The pallet 104 also differs from the pallet 62 in several importantrespects. First, the deck 108 is discontinued at spaced points 116corresponding to the positioning of the load bearing wall panels 50 and52. Second, the deck 108 and the beams 110 extend beyond one of thesupport points 114 to form a cantilever portion 118 of the pallet 108.At least some of the tension members 112 extend through plastic tubes120 or are otherwise disengaged from the material of the beams 110 inthe cantilever portion 118. This is necessary in order that the portion118 can be supported in cantilever fashion.

The installation of the service core 102 is illustrated in FIG. 10. Thepicking bars 78 of the lifting and position-ing apparatus shown in FIGS.11 and 12 are engaged with the beams 110 of the pallet 104 at pointsadjacent the support points 114. At the end of the pallet 104 comprisingthe cantilever portion 118, a picking bar 78 may be positioned at apoint located outside the positioning of the load bearing wall panel 50.Therefore, no problem is encountered in removing the pick

1. The method of fabricating a habitable building including dwelling units situated one above the other including the steps of: installing all of the kitchen, bathroom and temperature control facilities for a dwelling unit on a prestressed concrete pallet; mounting the pallet between the upper ends of a pair of prestressed concrete load bearing walls with one end of the pallet substantially in engagement with one of the load bearing walls; and forming a fire barrier between the opposite end of the pallet and the other load bearing wall.
 2. The method of fabricating a habitable building according to claim 1 further characterized by forming an enclosure on the pallet which extends substantially the entire length and width of the pallet, and wherein the fire barrier forming step is characterized by extending a length of fire proof material between the portion of the enclosure at the opposite end of the pallet and the other load bearing wall.
 3. The method of fabricating a habitable building according to claim 2 wherein the fire barrier forming step is further characterized by securing a length of fire proof material between the portion of the enclosure at the opposite end of the pallet and the upper surface of the pallet and securing the length of fire proof material between the upper end of the prestressed concrete load bearing walls and another portion of the load bearing wall.
 4. The method of fabricating a habitable building according to claim 1 wherein the fire barrier forming step is further characterized by positioning a length of fire proof material between the upper surface of the prestressed concrete pallet and the upper surface of the adjacent load bearing wall and extending the entire width of the prestressed concrete pallet.
 5. A multi-family dwelling unit comprising: a first pair of spaced, substantially vertically extending prestressed concrete load bearing wall panels; a first prestressed concrete pallet supported by the first pair of load bearing wall panels and extending between the upper ends thereof; an enclosure formed on the first prestressed concrete palleT and extending the entire length and width thereof; fire retarding means extending between one end of the first prestressed concrete pallet and the adjacent load bearing wall panel and extending substantially the entire width of the first prestressed concrete pallet; a second pair of spaced, substantially vertically extending prestressed concrete load bearing wall panels mounted on the upper ends of the first pair of wall panels and enclosing the opposite ends of the enclosure on the first concrete pallet; and a second prestressed concrete pallet extending between and supported by the upper ends of the second pair of prestressed concrete pallet load bearing wall panels.
 6. The multi-family dwelling unit according to claim 5 wherein the fire retarding means comprises a body of fire retarding material gripped between the first prestressed concrete pallet and one end of the enclosure thereon and between the upper surface of the adjacent one of the first pair of wall panels and the lower surface of the adjacent one of the second pair of wall panels.
 7. The multi-family dwelling structure according to claim 5 wherein the enclosure comprises complete mechanicals for two dwelling units and further including a fire barrier wall extending continuously between the second pair of wall panels and the first and second prestressed concrete pallets and separating the two sets of mechanicals within the enclosure.
 8. The multi-family dwelling structure according to claim 7 wherein at least the second prestressed concrete pallet includes at least one depending beam and wherein he fire barrier wall includes opposed members for receiving the depending beam and thereby extending the fire barrier wall to the second prestressed concrete pallet.
 9. The multi-family dwelling structure according to claim 7 wherein the fire barrier wall comprises a stub wall mounted for sliding movement outwardly to engage one of the panels comprising the second pair of wall panels and thereby extending the fire barrier wall continuously to said panel. 